Make PrivateTmp dirs also inaccessible from the outside

Currently, PrivateTmp=yes means that the service cannot see the /tmp
shared by rest of the system and is isolated from other services using
PrivateTmp, but users can access and modify /tmp as seen by the
service.

Move the private /tmp and /var/tmp directories into a 0077-mode
directory. This way unpriviledged users on the system cannot see (or
modify) /tmp as seen by the service.

2 files changed, 21 insertions, 19 deletions

diff --git a/src/core/execute.c b/src/core/execute.c
index 18e25fa6e6..bc876a3292 100644
--- a/src/core/execute.c
+++ b/src/core/execute.c
@@ -40,6 +40,7 @@
 #include <sys/poll.h>
 #include <linux/seccomp-bpf.h>
 #include <glob.h>
+#include <libgen.h>
 
 #ifdef HAVE_PAM
 #include <security/pam_appl.h>
@@ -1551,19 +1552,22 @@ void exec_context_init(ExecContext *c) {
 }
 
 void exec_context_tmp_dirs_done(ExecContext *c) {
-        assert(c);
+        char* dirs[] = {c->tmp_dir ? c->tmp_dir : c->var_tmp_dir,
+                        c->tmp_dir ? c->var_tmp_dir : NULL,
+                        NULL};
+        char **dirp;
 
-        if (c->tmp_dir) {
-                rm_rf_dangerous(c->tmp_dir, false, true, false);
-                free(c->tmp_dir);
-                c->tmp_dir = NULL;
-        }
+        for(dirp = dirs; *dirp; dirp++) {
+                char *dir;
+                rm_rf_dangerous(*dirp, false, true, false);
 
-        if (c->var_tmp_dir) {
-                rm_rf_dangerous(c->var_tmp_dir, false, true, false);
-                free(c->var_tmp_dir);
-                c->var_tmp_dir = NULL;
+                dir = dirname(*dirp);
+                rmdir(dir);
+
+                free(*dirp);
         }
+
+        c->tmp_dir = c->var_tmp_dir = NULL;
 }
 
 void exec_context_done(ExecContext *c, bool reloading_or_reexecuting) {
diff --git a/src/core/namespace.c b/src/core/namespace.c
index ceeed2e1ae..972380abc0 100644
--- a/src/core/namespace.c
+++ b/src/core/namespace.c
@@ -183,22 +183,20 @@ int setup_tmpdirs(char **tmp_dir,
         assert(tmp_dir);
         assert(var_tmp_dir);
 
-        r = create_tmp_dir(tmp_dir_template, 0000, true, tmp_dir);
+        r = create_tmp_dir(tmp_dir_template, tmp_dir);
         if (r < 0)
-                goto fail2;
+                return r;
 
-        r = create_tmp_dir(var_tmp_dir_template, 0000, true, var_tmp_dir);
-        if (r < 0)
-                goto fail1;
-
-        return 0;
+        r = create_tmp_dir(var_tmp_dir_template, var_tmp_dir);
+        if (r == 0)
+                return 0;
 
-fail1:
+        /* failure */
         rmdir(*tmp_dir);
+        rmdir(tmp_dir_template);
         free(*tmp_dir);
         *tmp_dir = NULL;
 
-fail2:
         return r;
 }